1. Field of Invention
The invention relates to the field of masonry construction. In particular, the invention relates to the field of construction of masonry "cavity" walls having an inner structural wall and an outer veneer wall and an air-space cavity between the structural wall and the veneer wall. More particularly, the invention relates to the problem of relieving moisture build-up in the air-space cavity by providing for adequate continuing drainage of moisture condensate to the outside of the outer wall. More particularly still, the invention relates to a device for preventing the obstruction of drainage weep holes in masonry cavity walls by wet and dry mortar and other construction debris during and after construction and to a method for use of such a device in masonry cavity wall construction.
2. Prior Art
In the field of masonry cavity wall construction, it is well know that moisture, largely in the form of condensation, tends to form and collect in the cavity between the inner construction wall and outer veneer wall. In general, the inner wall of a cavity wall construction is the load-bearing element and may be made of masonry block, framed in wood, or framed in metal; typically it has an innermost surface of wallboard, wood paneling, or tile. The outer veneer wall is usually made of mortared brick or masonry stone. In general, the inner, load-bearing wall is constructed first, and the outer veneer wall afterward. The distance between the inner and outer walls forming the air-space cavity is typically from one inch to three inches. Moisture, if allowed to collect and remain in the air-space cavity, will lead to a number of undesirable effects in the construction materials ranging from cosmetic discoloration to rot and disintegration leading to structural weakening.
Moisture accumulation in cavity-type walls is a well-known problem. (See, e.g., U.S. Pat. No. 2,147,035 issued to Henderson in 1939, which teaches drains installed within walls made of hollow-core masonry block.) Awareness of this problem has lead to the nearly universal practice of constructing such walls to have a number of drainage weep holes leading from the air-space cavity to outside of the outer veneer wall. Such weep holes are left along the base of the wall and also along the tops of doorways, window openings, and other breaks through the wall that create surfaces where moisture condensate may collect.
In general, weep holes are simply gaps in the mortar beneath the bottom course of brick and/or between some of the adjacent bricks in the bottom course. In some instances the holes may be lined with tubing or may be created by a device built into the structure, such as the weep hole form taught by Johnson (U.S. Pat. No. 2,934,931 issued 1960), which includes some minimal protection against debris clogging the formed weep hole. However, such weep-hole forms tend to be expensive and, being usually of metal, tend to corrode. The installation of such forms also adds an extra step in the building process, increasing labor costs; thus, they are not often employed.
Regardless of the method used to provide weep holes, however, it is the primary purpose of such weep holes to provide a path for drainage of condensate from the within wall cavity to the outside. Since intrusion of water vapor both though the weep holes, but principally though gaps, cracks, and cuts, however tiny, provides a continually renewing source of moisture condensate, it is accepted as essential that the drainage weep holes remain unobstructed over the life of the wall. Thus, a number of devices and methods have been taught that deal with keeping the weep holes clear and functional as drainage passages.
Sources of weep-hole-obstructing debris are present during construction and also after construction. During construction the primary source of such debris is excess, wet mortar squeezed from between courses of bricks as they are being laid. Wet mortar that exudes from between courses on the outside of the wall is removed by scraping it away with the mason's trowel; that which is extruded from between courses on the inside, however, cannot be so removed, due to the narrowness of the air-space cavity, and some of it will fall to the bottom of the cavity where the weep holes are. Also other construction debris, such as wall board trimmings, sawdust, and nails, may fall between the inner and outer walls into the air-space cavity during construction.
Early solutions to this problem depended on applying a secondary use of wall ties. Wall ties were usually made of metal rod worked into various shapes and designs that were attached (in a masonry wall by being mortared between courses) to both the inner and outer wall to tie the walls together. Such a wall-tie-dependent device was disclosed by Xanten (U.S. Pat. No. 2,705,887 issued 1955), in which the wall tie was formed to provide a bight in the cavity between the walls to hold in place a V-shaped trough of sufficient length to span two or more such ties. The troughs, having handles by which they could be removed from above, would be set across previously installed wall ties, below the site where bricks were then currently being laid, to catch the wet mortar and other debris falling into the cavity during construction. The troughs would then be extracted, emptied, and moved as work progressed. Obviously, however, this process created a number of extra work steps, added significantly to construction time and labor costs, and provided no continuing protection after construction was complete.
A later scheme of Ballantyne (U.S. Pat. No. 4,852,320 issued in 1989) provides for a plurality of individual mortar-collecting devices to be set on or installed with wall tie members. The upper surface of each device is inclined sufficiently to allow water to run off, but no so severely as to permit wet mortar to slide off. The devices are installed adjacent to the inside of the mortared wall and spaced in staggered rows, so that no vertically clear path remains for mortar to fall without hitting at least one of the devices. While they were effective in catching wet mortar, however, such devices were ineffective in preventing the excursion of dry debris to the bottom of the cavity during and after construction. Also, in order to provide sufficient protection along the length of the wall, either a large number of small devices, or a smaller number of larger devices of this type are required. This requirement not only adds steps--thus increasing time and labor costs--to the construction process, but also increases construction material costs. This increase in material cost is exacerbated, currently, because modern construction techniques have made wall ties largely unnecessary in cavity wall construction, making such wall-tie-dependent devices especially undesirable.
New materials provide alternatives both to expensive mechanical solutions to debris collection and to dependence on particular construction features, and may obviate the necessity of additional construction steps. One such class of materials consists of a non-woven coarse mesh of polymer fiber. Such non-degradable fibers tend to maintain their shape and strength characteristics over time under the range of normal environmental conditions, and a non-woven mesh of sufficient coarseness does not interfere with air circulation nor impede the flow of condensate, but provides an interfering matrix of fibrous collectors sufficient to catch and hold both wet and dry debris produced both during and after construction. A number of devices and methods employing such materials have been set out.
A system of weep hole obstruction prevention in masonry cavity walls disclosed by Atkins (U.S. Pat. No. 5,598,673 issued in 1997) teaches that the entire air-space cavity of a cavity wall be filled with the type of non-woven mesh described above. This system is obviously effective in preventing the introduction of all types of construction and post construction debris to the bottom of the air-space cavity to obstruct the flow of condensate through the weep holes. However, the system of Atkins requires the use of a massive amount of mesh material. As with previously described devices and methods, this requirement greatly increases construction material costs, not only from the amount of mesh material needed, but also from the need to affix the mesh material to a solid backing sheet material in order to support the mesh and maintain its vertical dimension to be coincident with the vertical dimension of the wall. Further, installation of this system increases labor costs.
Another system for the prevention of the accumulation of debris from weep holes disclosed by Laska (U.S. Pat. No. 5,860,259; 1999) teaches the use of an insulating layer in conjunction with a matting or, alternatively, with a solid plastic material. While Laska teaches that the matting may be made from strands of polymer or copolymer, the only structure disclosed for this matting is a complete filling of the space between the outer with and the insulating layer. This construction is similar to that of Atkins with the addition of an insulating layer in the space between the wythes. Besides the added cost of filling the entire void with fiber, falling mortar readily accumulates along the top edge of the matting in this embodiment of Laska. As a result, the draining function of the system is frustrated.
Laska also teaches a drain section made from a solid plastic having a "waffled" cross-section. Because the majority of the depth of the space between wythes is filled by the insulating layer, the drain function is highly dependent on the void space occupied by the protrusions. If the diameter of protrusions is too wide, then the mortar falling into the drain will bridge the gaps between the protrusions. Because the volume of the inter-wall space is substantially filled by the insulating layer, the volume of mortar falling into the drain is forced to move parallel to the walls to a greater degree than if the insulating layer was absent. Consequently, an upper limit exists on the percentage of void space that the solid-plastic waffle-protrusions can occupy. If this limit is exceeded the drain function markedly decreases, or even ceases all together. Laska is, by practicality, constrained to using protrusions that slope downward or are rounded so as to prevent bridging.
The inventor of the present invention has used non-woven polymer-fiber mesh filter material to address the problem under discussion. Using sheets of such material--as are shown in FIG. 1 (Prior Art)--having thicknesses less than the width of the air-space cavity and installed to various heights above the weep holes, the inventor reached three significant conclusions:
(a) as a practical matter, it is not necessary to extend the debris-blocking action to heights greater than 9 to 18 inches above the weep holes; PA1 (b) readily-available non-woven polymer-fiber mesh material has more than sufficient strength to maintain its own shape under the weight of the greatest amount of debris that could be expected to load it in a mortar wall, that is that there was no need for external support such as would be provided by affixing a solid backing to the mesh or by making the sheet thickness equal to the depth of the cavity; PA1 (c) this mesh material is readily available in mesh densities sufficient to prevent penetration by construction and post-construction debris while continuing to provide for the free flow of moisture condensate and air.
Also, the inventor observed from his work that construction debris can easily be removed manually until the height of the outer veneer wall reaches about 9 to 18 inches above the base location of the weep hole, the height depending on the depth--i.e., the distance between the inner and outer walls--of the particular air-space cavity. This meant that the debris-blocking device did not have to be installed until after the construction had passed this height. This meant in turn that the masons do not have to contend with the presence of the mesh or other device immediately abutting the area of the wall that they are working on.
After the outer veneer wall has been raised to a height of 9 to 18 inches, the sheet is set into the cavity so that its lower edge is against the inner wall and its upper edge then leans against the outer wall, as shown in FIG. 1 (Prior Art). Experience with this configuration has shown that, properly installed, it provides more than sufficient debris-collection surface area. This means that its permeability to liquid condensate (and air) is not significantly affected even after it has caught, and therefore accumulated, its full load of debris. Nevertheless, it can be installed incorrectly relatively easily, namely by placing its bottom end against the weep-hole side of the bottom plane rather than the opposite side. This means that a certain level of supervisory oversight must be maintained to ensure proper installation, as is always true when it is possible to install something incorrectly. Furthermore, these extended mesh bodies, having uniform thickness as well as width and depth, take up a significant volume during transport and storage.
Mortar debris collection devices disclosed by Sourlis (U.S. Pat. No. 5,230,189 issued in 1993) ["Sourlis I"] and Sourlis (U.S. Pat. No. 5,343,661 issued in 1994) ["Sourlis II"] generally employ one or more non-woven fiber mesh sheets that together have a thickness equal to the depth of the air-space cavity. While Sourlis I and Sourlis II teach devices and systems which are generally installed within the bottom of the airspace cavity to a height of only several courses of brick or masonry stone veneer wall, some of those applications require that the sheets be cut to specific shapes, others require additional mounting devices, and still others disclose systems of mechanical projections that must be mechanically affixed to or through solid backing materials. In every case, the Sourlis I and Sourlis II devices require a number of fabrication and/or installation operations that increase both the cost of the devices and the cost of time and labor required to install them. Also, the bulk of these devices require substantial shipping and storage resources.
What is needed is, then, is a debris-collecting device for preventing the obstruction of weep holes that is less expensive to install than are the prior art devices. What is further needed is such a debris-collecting device that requires less space during transportation and storage than do the prior art devices. What is yet further needed is such a debris-collection device that can be installed within masonry cavity walls with no need for supervisory oversight to ensure that it is installed properly.